Geography 316.01
SFSU
Dr. B.A. Holzman
Past Mass Extinctions
Past Extinction/Causes
„ Effects, future implications
„ Major Events
„ Pleistocene events
„
OrdovicianOrdovician-Silurian extinction,
extinction, about 439
million years ago, caused by a drop in sea
levels as glaciers formed, then by rising sea
levels as glaciers melted. The toll: 25 percent
of marine families and 60 percent of marine
genera.
„
Late Devonian extinction,
extinction,
about 364 million years ago,
cause unknown. It killed 22
percent of marine families
and 57 percent of marine
genera. Little is known about
land organisms at the time.
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Geography 316.01
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Dr. B.A. Holzman
PermianPermian-Triassic extinction,
extinction,
about 251 million years ago..
The PermianPermian-Triassic
catastrophe was Earths worst
mass extinction, killing 95
percent of all species, 53
percent of marine families, 84
percent of marine genera and
an estimated 70 percent of
land species such as plants,
insects and vertebrate
animals.
Past Mass Extinctions
Fig. I. Reconstructions of the ancient seabed in southern China immediately before (a) and after (b) the Permo–
Permo–Triassic mass
extinction. Note the richness of reef life and the burrowing infauna before the crisis, and the absence of such species after. A
marine fauna of 100 or more species is reduced to four or five.
five.
Past Mass Extinctions
CAUSES
VOLCANIC ERUPTIONS:
ERUPTIONS:
Fire, smoke, debris into atmosphere
Æ Loss of land, lava flow
Æ Aerosols in air become acid rain
Æ
EXAMPLE:
EndEnd-Permian Extinctions, 250 mya
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Geography 316.01
„
„
SFSU
Dr. B.A. Holzman
End Triassic extinction,
extinction, roughly 199
million to 214 million years ago, The
death toll: 22 percent of marine
families, 52 percent of marine genera.
Vertebrate deaths are unclear.
CretaceousCretaceous-Tertiary extinction,
extinction, about 65
million years ago,. The extinction killed 16
percent of marine families, 47 percent of
marine genera (the classification above
species) and 18 percent of land vertebrate
families, including the dinosaurs.
Past Mass Extinctions
CAUSES
ASTEROID HITS EARTH:
EARTH:
Æ“Impact Theory”
Theory”
Æ Creates tsunamis, fires, launches debris &
smoke into atmosphere
Æ Darkness lasts for years, “impact winter”
winter”
EXAMPLE: CretaceousCretaceous-Tertiary extinctions
(KT Boundary), 65 mya
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Geography 316.01
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Dr. B.A. Holzman
Past Mass Extinctions
CAUSES
SEA LEVEL CHANGE:
CHANGE:
ÆInterior continental seas drain
Æ Drop in primary production, collapse in food chain
Æ Change in topography, terrain, affects wind patterns,
climate
Æ Seasonal climates develop, deserts emerge
EXAMPLE: KT Boundary
Past Mass Extinctions
CAUSES
CLIMATE CHANGE:
CHANGE:
Æ
Æ
Cooling,
Cooling, from glaciation or darkness
Warming, from greenhouse gases
EXAMPLE:
Pleistocene Megafauna extinctions
Past Mass Extinctions
CAUSES
HUMANS AS HUNTERS
Æ Overkill Theory for Pleistocene megafauna
extinctions
HUMANS AS FARMERS
Æ Habitat destruction and fragmentation from
human population
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Geography 316.01
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Dr. B.A. Holzman
Past Mass Extinctions Effects
w
Evolutionary impacts:
impacts: debate about the role of mass
extinction events in spurring new evolutionary
directions and opportunities.
w
Biodiversity:
Biodiversity: While the loss of biodiversity is
catastrophic at the time of the event, it has rebounded
each time, and perhaps will rebound again despite the
current rate of extinctions
Quaternary Events/Extinctions of the Past
Where have all the Megafauna gone.....?
I. The Facts: once there were megafauna….
now there are none
Extinctions occurred
Climate Changed
Humans came to North America
II. The Explanations
Climate- Evolution
Overkill (P.A. Martin)
Other Alternatives (a compromise?)
III. Conclusions
Extinctions happen everyday
Will we ever know..do we care ????
Megafaunal Extinction
Megafauna: > 44kg (100 lbs)
mostly large grazers, browsers and carnivores
Pleistocene: 2 MYA- 12KYA
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Geography 316.01
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Dr. B.A. Holzman
Mastodon
Some examples
Mammoth
Doedicurus (Glyptodon)
Woolly rhinoceros
(Coelodonta antiquitatis)*
Beautiful armadillo (Dasypus bellus)
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Dr. B.A. Holzman
Giant Ground Sloth
Shasta Ground Sloth
American camel
Stag Moose
Muskoxen
Irish Elk
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Dr. B.A. Holzman
Dire wolf
Short faced bear
Smilodons
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Dr. B.A. Holzman
Extinctions occurred without replacement !!!!!!!!!!!!!
Mammoths (Mammuthus) and American Lions
(Felis atrox) in the late Pleistocene of Alaska
Explanations:
„
„
Climate change
Pleistocene Overkill
Human occupation of N. America directly
caused extinction of larger mammals
Climatic Change?:
• Extinctions occurred with an
episode of climatic change
• Magnitude of change are correlated with the
magnitude of extinctions
• Mechanisms identified that link climatic change
with extinctions given with type of change,
extinctions would be the expected result
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Geography 316.01
SFSU
Dr. B.A. Holzman
Many combined reasons for extinction
based on climate changes
„
„
„
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Increased Seasonality
Decrease plant diversity
Increased anti herbivory mechanisms
Restricted resources
Gestation/Breeding and Birth (Kiltie)
Increased Seasonality
•Axelrod (1967) argues early interglacials
were more equitable than the early
Holocene
.
•It is this loss of equitability that caused
extinction
•Decrease plant diversity
Plaid vs. Stripes
Gunthrie argues changing seasonal regimes at
the end of the Pleistocene led to an increasingly
homogeneous plant community with decreased
quality and quantity of plant resources available
Plaids: mongastrics:
mammoths, horses,
camels
vs.
Stripes:
Stripes: ruminants:
antelopes, sheep,
bison
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Geography 316.01
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Dr. B.A. Holzman
Anti-herbivory mechanisms
•Plants may have evolved with
increase anti-herbivory mechanisms
•Restricted resources led to
decreased faunal diversity, body size
and led to extinction
Gestation/Breeding and Birth (Kiltie)
„
„
Shifting birthing and breeding to accommodate
drastic climatic changes isn't feasible for
megafauna in short time spans.
Having offspring during a cold season or
delaying mating may comprise a population’
population’s
viability
Social Organs
Giant Irish Elk
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Dr. B.A. Holzman
Extinctions have occurred
before
Or was it people??
Paul Martin: 1973
The Discovery of America
„
Pleistocene Overkill
Human occupation of N.
America directly caused
extinction of larger mammals.
Pleistocene Overkill
„
Gradual destruction of fauna over thousands of
years
„
Suddenly in as little as 100 years
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Geography 316.01
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Dr. B.A. Holzman
Nature of human impact classified
as 3 types:
BLITZKRIEG Effect
INNOVATION Effect
ATTRITION Effect:
Blitzkrieg: rapid deployment
of human populations w/ big
game hunting= rapid demise of
big game
Innovation: long established
human populations adopt new
hunting technologies and erase
fauna stressed by climate.
Advanced technology- Clovis point
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Geography 316.01
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Dr. B.A. Holzman
ATTRITION: extinction takes place relatively slowly
after a long history of human activity b/c loss of habitat
and competition for resources
in Conclusion.............................
„
It seems to me that it is a combination of factors.
Populations could have been stressed to the breaking
point due to climatic changes and the consequent
changes in plant life , gestation and fertility. Then
humans came along and were the final straw.
„
It seems implausible to rule out one over the other,
when we have evidence of the two occurring
simultaneously.
Historic examples
Moa –New Zealand
Elephant Bird -- Madagascar
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Geography 316.01
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Dr. B.A. Holzman
More recent extinctions
Colonization
„ Hunting
„ Habitat Loss
„ Invasions
„
Mass Extinctions--Today
„
“On average, one
extinction happens
somewhere on earth
every 20 minutes.”
minutes.”
(Levin, 2002. p6)
„
“Ecologists estimate
that half of all living
bird and mammal
species will be gone
within 200 or 300
years.”
years.”
(Levin, 2002. p6)
Mass Extinctions:
FUTURE IMPLICATIONS
„
„
„
Do today’
today’s extinction rates compare?
Will human disturbance lead to ecosystem
decay and mass extinction?
Or will it lead to fragmented “islands”
islands” that
lead to more speciation and evolution?
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